It seems to be provider specific. Many JMS providers will treat "Receives the next message if one is immediately available" literally - i.e. not to wait for a request/response with the broker to check if there is a message available for processing. This is what ActiveMQ does and a number of other JMS providers do the same - but its provider specific.
At the very least you should wait some period of time (say 1 second) after creating your consumer before issuing a receiveNoWait() if you want your code to work with most JMS providers - or use receive(1000) on the first call - then use receiveNoWait() afterwards etc. 2008/8/26 Jecsiac <[EMAIL PROTECTED]>: > >>receiveNoWait() is not meant to wait for a message to arrive. In >>ActiveMQ creating a receiver does not block until messages are >>received. > >>i.e. its not really JMS compliant to use receiveNoWait() and not >>expect nulls to come back if you've not really left much time for the >>JMS provider to actually find the messages and return them over the > > JMS 1.1 Specification has no words on receiveNoWait() (at least in it's PDF > document). And in JMS 1.1 API document, it just said: > > receiveNoWait > public Message receiveNoWait() > throws JMSException > Receives the next message if one is immediately available. > Returns: > the next message produced for this message consumer, or null if one is not > available > Throws: > JMSException - if the JMS provider fails to receive the next message due to > some internal error. > > Maybe it is some amphibolous. So I think my expectation could also be > proper: There're 2000 messages in the queue, and the message I want to find > is just in them, so why receiveNoWait() gives me a null? Of course, the > provider needs time to find out the message. But in contrast with receive(): > > receive > public Message receive() > throws JMSException > Receives the next message produced for this message consumer. > This call blocks indefinitely until a message is produced or until this > message consumer is closed. > > If this receive is done within a transaction, the consumer retains the > message until the transaction commits. > > Returns: > the next message produced for this message consumer, or null if this message > consumer is concurrently closed > Throws: > JMSException - if the JMS provider fails to receive the next message due to > some internal error. > > It seems NoWait could means no 'blocks indefinitely until a message is > produced' —— but should it include the time the provider needs to find out > the message? No more words. So maybe it is some amphibolous. > > -- > View this message in context: > http://www.nabble.com/Problem-with-Selector-tp19157015p19161717.html > Sent from the ActiveMQ - User mailing list archive at Nabble.com. > > -- James ------- http://macstrac.blogspot.com/ Open Source Integration http://open.iona.com
